This invention relates generally to the construction of spring assemblies or the like. More particularly, it relates to the manufacture of spring cores of strings of pocketed coil springs for use in mattresses, seat cushions or the like.
Mattress spring core construction over the years has been a continuously improving art with advancement in materials and machine technology. A well known form of spring core construction is known as a Marshall spring construction wherein metal coil springs are encapsulated in individual pockets of fabric and formed as elongate or continuous strings of pocketed coil springs. In an early form, these strings of coil springs were manufactured by folding an elongate piece of fabric in half lengthwise to form two plies of fabric and stitching transverse and longitudinal seams to join the plies of fabric to define pockets in which the springs were enveloped.
Recently, improvements in spring core constructions have included the use of fabrics which are thermally or ultrasonically weldable to themselves. By using such welding techniques, these fabrics have been used advantageously on a mass production basis to more efficiently manufacture strings of individually pocketed coil springs wherein transverse and longitudinal welds replace stitching to form pockets encapsulating the springs.
The manufacture of strings of pocketed coil springs with a single spring in each pocket is well known in the art and, for example, such machines and systems are commercially available from Spuhl AG in Switzerland. Examples of such machines include the Spuhl TF 90, 190 and 290 series machines. Another known system for pocketing coil springs is disclosed in U.S. Pat. No. 4,439,977 which is hereby incorporated by reference in its entirety.
Once strings of pocketed coil springs are manufactured, they may be assembled to form a spring core construction for a mattress, cushion or the like by a variety of methods. For example, multiple or continuous strings may be arranged in a row pattern corresponding to the desired size and shape of a mattress or the like. The adjacent rows of strings may be interconnected by a variety of methods. The result is a unitary assembly of pocketed coil springs serving as a complete spring core assembly. In an early form, the rows or strings of such a unitary assembly of pocketed coil springs were interconnected by mechanical fasteners such as staples, clips, or the like. More recently, various forms of adhesives applied to the side surface of a first row or string of pocketed coil springs are used to bond that row or string to an adjacent row or string and after this is repeated for multiple strings to thereby construct a unitary spring core assembly.
One example of a spring core assembly constructed from a plurality of strings of pocketed coil springs glued together is disclosed in U.S. Pat. No. 4,578,834. Each of the pocketed coil springs in the spring core disclosed in that patent includes a discrete hot melt adhesive deposit on the sidewall thereof. Specific shortcomings associated with that design include the limited bonding strength produced between the adjacent rows of pocketed coil springs because of the individualized discrete deposits of adhesive. Additionally, the requirement of cycling the adhesive applicator rapidly on and off while manufacturing such a spring core assembly can be problematic. Such demands on the adhesive applicator result in frequent maintenance problems and limited and unreliable production capacity.
Spring core constructions manufactured with adjacent strings of pocketed coil springs adhesively bonded together are also disclosed in U.S. Pat. Nos. 4,566,926 and 5,637,178. The system disclosed in the '926 patent includes a hot melt adhesive applicator having a plurality of spray nozzles which apply hot melt adhesive to a selected portion of each pocketed coil spring. The applicator moves longitudinally along the length of a stationary string of pocketed coil springs to apply the hot melt adhesive. On the other hand, the system shown in the '178 patent requires the assembly of spring core constructions from strings of pocketed coil springs in which a first string of coil springs is moved on a conveyor and coated with adhesive sprayed from a fixed adhesive applicator. The manufacturing capacity of each of these systems is limited because of the requirement for a fixed adhesive applicator or a stationary string of pocketed coil springs onto which the adhesive is applied. In those systems, the production of spring core assemblies is the result of a discontinuous or batch like process. Furthermore, the adhesive is not efficiently and optimally applied to the strings of pocketed coil springs for a uniform and unitary spring core assembly.
Further, known systems and methods for adhesively bonding strings together typically bond each pocketed coil spring to each adjacent pocketed coil spring in the adjacent rows. As such, the bonding systems and methods do not allow for customization of the spring unit by varying the bonding scheme to permit differential movement of selected pocketed coil springs relative to selected pocketed springs in adjacent strings or rows.
These identified and other systems provide limited opportunities to manufacture spring core assemblies from pocketed coil springs. There is a need to provide a system and method which can be utilized on a production basis for more complete automation of the procedure for the expeditious and efficient manufacture of spring core assemblies from strings of pocketed coil springs adhesively bonded together while allowing for customization of the spring unit and portions thereof.